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1. Description of Related Art
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2. Field of the Invention
The present invention relates to mobile communications systems, and more specifically, to recovery of a home location register from a fault in a system where a gateway location register serves a visitor location register.
FIG. 1 illustrates a wireless communication system in accordance with the Global System for Mobile communication (GSM) standard. The GSM standard is designed to provide a uniform interface which allows mobile communication subscribers of various countries to operate their mobile devices regardless of the current location of the mobile subscriber. A mobile subscriber typically has a subscription with a network which is designated as the mobile subscriber""s home public land mobile network 110 (HPLMN). The HPLMN 110 has a home location register (HLR) 115 which contains, among other things, various information regarding the services provided to the mobile subscriber. When a mobile subscriber roams into a different network, which is referred to as a visited public land mobile network 120 (VPLMN), the VPLMN requires certain data regarding the mobile subscriber""s subscription. The data regarding the mobile subscriber""s subscription is also known as the mobile subscriber""s profile. The mobile subscriber""s profile is transferred from the HLR to a visitor location register (VLR) in the VPLMN 120.
In a GSM system mobile subscriber data is stored within the VLR that is associated with the mobile services switching center (MSC) that currently serves the mobile subscriber in order to reduce internetwork signaling between VLRs and HLRs. The decentralization of the VLRs within a GSM system (i.e., each MSC being equipped with a VLR) reduces intranetwork signaling as well. So, for example, if the mobile subscriber is roaming in an area of the VPLMN 120 which is controlled by the MSCNVLR 130, the HLR 115 will transfer the mobile subscriber""s profile to MSC/VLR 130. Similarly, if the mobile subscriber is roaming in an area controlled by MSC/VLR 135, the HLR 115 will transfer the mobile subscribers profile to MSCNVLR 135.
Although FIG. 1 illustrates the MSCNVLR as a single network node, one skilled in the art will recognize that the MSC and VLR can be implemented as separate network elements.
To increase the compatibility of GSM with other types of systems, it is anticipated that future versions of the GSM standard, also called Universal Mobile Telecommunications System (UMTS), will incorporate elements of other mobile communications systems. For example, the Japanese Personal Digital Cellular (PDC) system includes a network node which is used to reduce internetwork signaling known as a gateway location register (GLR). FIG. 2 illustrates an exemplary mobile communications system in accordance with the PDC system. Like a GSM system, a home network 210 includes an HLR 215 which contains the mobile subscriber""s profile. When a mobile subscriber roams into a visited network 220 the mobile subscriber""s profile is transferred to GLR 225. In GSM terms, the GLR can be described as a VLR for all mobile subscribers roaming from other networks. Hence, only one GLR is needed for each network.
FIG. 3 illustrates an exemplary UMTS system which incorporates the GLR of the PDC system. When a mobile subscriber of HPLMN 310 roams into VPLMN 320, the HLR 315 will transfer the mobile subscriber""s profile to GLR 325. Then, depending upon which area within the VPLMN 320 the mobile subscriber is roaming, the GLR 325 will transfer the mobile subscriber""s profile to the respective MSCNVLR 330, 335 or 340. The introduction of the GLR 325 into a GSM system reduces internetwork signaling because once the mobile subscriber roams into VPLMN 320, the HLR will only need to transfer the mobile subscriber""s profile to GLR 325. GLR 325 will be responsible for transferring the mobile subscriber""s profile to the proper MSC/VLR within VPLMN 320 as the mobile subscriber travels around the VPLMN 320.
The protocol used by GSM/UMTS systems for transferring data between VLRs and HLRs is the mobile application part (MAP). FIG. 4 illustrates a conventional method using the MAP protocols in a GSM system when an HLR is recovering from a fault. In step 405 the HLR loads the contents of its non-volatile backup memory into its dynamic memory. Next the HLR sends a MAP_RESET message to the VLRs to which the HLR""s mobile subscribers are currently associated as indicated by the information in the backup memory in accordance with step 410. The MAP_RESET request message includes the HLR number, which is the E.164 number of the HLR, and, optionally, an HLR identity (Id) list. The HLR Id list is a list of the possible combinations of leading digits of the IMSIs that belongto the concerned HLR, including Country Code (CC), network code and the leading digits of the National Destination Code (NDC). In step 415, the VLR determines which of the mobile stations that are currently served by the VLR are associated with the HLR which sent the MAP_RESET message. In conventional GSM systems there are two different ways for the VLR to determine which mobile stations are associated with a particular HLR. If the HLR Id list parameter is present in the MAP_RESET message the affected mobile subscribers can be identified as those mobile stations whose leading digits of their IMSI matches the digits of either of the HLR identities in the HLR Id list parameter. If the HLR Id list parameter is not present in the MAP_RESET message the affected mobile subscribers are derived using the HLR number in the MAP_RESET message, i.e., the affected mobile subscribers are those for which the HLR number stored in the mobile subscriber record in the VLR matches the HLR number received in the MAP_RESET message.
In step 420 the VLR sets the xe2x80x9cLocation Information Confirmed In HLRxe2x80x9d flag for all of the affected mobile stations to xe2x80x9cNot Confirmedxe2x80x9d. Setting this flag will force the VLR to perform a MAP_UPDATE_LOCATION service to update the HLR at the next authenticated radio contact with each affected mobile station. In step 425 the VLR waits for an authenticated radio contact from the concerned mobile subscriber. In step 430 the VLR determines whether it has received an authenticated radio contact from the concerned mobile subscriber. If the VLR has not received an authenticated radio contact from the concerned mobile subscriber, in accordance with the xe2x80x9cNoxe2x80x9d path out of decision step 430, the VLR continues to wait in accordance with step 425. If the VLR receives an authenticated radio contact from the concerned mobile subscriber the VLR sends a MAP_UPDATE_LOCATION message to the HLR indicating that the VLR is serving the concerned mobile subscriber in accordance with step 435. The location updates sent from the VLRs to the HLR will gradually restore and confirm the mobile subscriber data of the restarted HLR.
Since GLRs are optional elements within the UMTS system, MAP procedures must be completely independent of the presence or absence of GLRs in a network. Accordingly, by using an HLR interface towards the VLRs and a VLR interface towards the HLRs, the GLR should be completely transparent. However, because of the dual nature of the GLR in the network it may be difficult for the GLR to behave in a way which simultaneously will be perceived as VLR behavior by the HLRs, and as HLR behavior by the VLRs. One such case is the fault recovery behavior of the HLR.
In a conventional GSM UMTS system, if a GLR were added to a VPLMN containing a VLR, the HLR would send the MAP_RESET message to the GLR instead of the VLR. However, since the GSM MAP protocols do not account for a GLR in the network, and the PDC MAP protocols do not account for a VLR in the network, there are no procedures defining how an HLR should recover from a fault when some of its affected mobile subscribers are located in areas where a gateway location register serves a visitor location register.
Accordingly, it would be desirable to provide methods and apparatus for HLR fault recovery in a UMTS system including a gateway location register and a visitor location register. Further, it would be desirable for the HLR fault recovery to be performed without violating the GSM MAP protocol, i.e. using the specified message formats and not violating any specified message sequences.
According to exemplary embodiments of the present invention, methods and apparatus are provided for home location register fault recovery. A gateway location register receives a reset message from the home location register. The reset message contains a home location register number for the home location register. The gateway location register sends another reset message to a visitor location register. The another reset message includes a gateway location register number for the gateway location register. Alternatively, the another reset message includes a home location register number for the home location register and the home location register identity list.
In accordance with this aspect of the present invention the reset message and the another reset message can be MAP_RESET messages. In addition, the gateway location register can determine a mobile subscriber associated with the home location register, and the gateway location register determines that the visitor location register serves the mobile subscriber. Further, the reset message and the another reset message can include a home location register identity list. In addition, the visitor location register can identify affected mobile subscribers using either the gateway location register number or the home location identity list.
In accordance with another aspect of the present invention a gateway location register receives a reset message from the home location register, wherein the reset message includes a home location register number. A mobile subscriber associated with the home location register is determined by comparing a country code and national destination code of a mobile subscriber identity stored in a record associated with the mobile subscriber with a country code and national destination code of the home location register number. Alternatively, a mobile subscriber associated with the home location register can be determined by comparing the home location register number received in the reset message with a home location register number stored in a mobile subscriber record in the gateway location register.
In accordance with this aspect of the present invention the gateway location register determines a visitor location register which is currently serving the mobile subscriber. Another reset message is sent to a visitor location register which has been determined to be currently serving the mobile subscriber. Further, the another reset message is received by the visitor location register and it is determined whether there is a home location register identity list in the another reset message.